Method and apparatus for automated synthesis of multi-channel circuits

ABSTRACT

Methods and apparatuses to automatically generate time multiplexed multi-channel circuits from single-channel circuits. At least one embodiment of the present invention automatically and efficiently synthesize multi-channel hardware for time-multiplexed resource sharing by automatically generating a time multiplexed design of multi-channel circuits from the design of a single-channel circuit. Channel specific elements of the single-channel design (e.g., registers and memories) are replaced with corresponding elements of N-times more capacity for pipelining the signal processing for multiple channels.

This application is a continuation of co-pending U.S. patent applicationSer. No. 10/407,678, filed on Apr. 4, 2003.

FIELD OF THE INVENTION

The invention relates to digital circuits, and more particularly to theautomated synthesis of multi-channel hardware.

BACKGROUND OF THE INVENTION

For the design of digital circuits (e.g., on the scale of Very LargeScale Integration (VLSI) technology), designers often employcomputer-aided techniques. Standard languages such as HardwareDescription Languages (HDLs) have been developed to describe digitalcircuits to aid in the design and simulation of complex digitalcircuits. Several hardware description languages, such as VHDL andVerilog, have evolved as industry standards. VHDL and Verilog aregeneral-purpose hardware description languages that allow definition ofa hardware model at the gate level, the register transfer level (RTL) orthe behavioral level using abstract data types. As device technologycontinues to advance, various product design tools have been developedto adapt HDLs for use with newer devices and design styles.

In designing an integrated circuit with an HDL code, the code is firstwritten and then compiled by an HDL compiler. The HDL source codedescribes at some level the circuit elements, and the compiler producesan RTL netlist from this compilation. The RTL netlist is typically atechnology independent netlist in that it is independent of thetechnology/architecture of a specific vendor's integrated circuit, suchas field programmable gate arrays (FPGA) or an application-specificintegrated circuit (ASIC). The RTL netlist corresponds to a schematicrepresentation of circuit elements (as opposed to a behavioralrepresentation). A mapping operation is then performed to convert fromthe technology independent RTL netlist to a technology specific netlist,which can be used to create circuits in the vendor'stechnology/architecture. It is well known that FPGA vendors utilizedifferent technology/architecture to implement logic circuits withintheir integrated circuits. Thus, the technology independent RTL netlistis mapped to create a netlist, which is specific to a particularvendor's technology/architecture.

In designing a circuit, transformations are frequently performed tooptimize certain design goals. For example, transformations may beperformed to reduce the area used by a circuit. Folding transformationis one of the systematical approaches to reduce the silicon area used byan integrated circuit. By executing multiple algorithm operations on asingle function unit, the number of functional units in theimplementation can be reduced. More details about foldingtransformations can be found in “VLSI digital signal processing systems:design and implementation”, by Keshab K. Parhi, Wiley-Interscience,1999.

Time multiplexed resource sharing has been used in the digitalcircuitry. For example, Peripheral and Control Processors (PACPs) of theCDC 6600 computer, described by J. E. Thornton in “Parallel Operationsin the Control Data 6600”, AFIPS Proceedings FJCC, Part 2, Vol. 26,1964, pp. 33-40, share execution hardware by gaining access to commonresources in a round-robin fashion. Another example about resourcesharing for multi-channel filters can be found in: Jhon J. Leon Franco,Miguel A. Melgarejo, “FPGA Implementation of a Serial Organized DAMultichannel FIR Filter”, Tenth ACM International Symposium on FieldProgrammable Gate Arrays, Monterey, Calif., Feb. 24-26, 2002.

A conventional folding algorithm can be used to automatically generate adesign with time-multiplexed resource sharing from a given design. Aconventional folding algorithm identifies the multiple algorithmoperations that can be time multiplexed to a single functional unit toreduce the number of functional units (e.g., adders, multipliers).However, given a Digital Signal Processing (DSP) design, a conventionalfolding algorithm spends a significant amount of time in extractingparallelism and dependencies and in optimizing computation schedules.The complexity of hardware synthesis grows super-linearly with thenumber of logic units involved in the computation. Thus, the larger thedesigns, the harder it is to optimize and transform the circuitry.

SUMMARY OF THE DESCRIPTION

Methods and apparatuses to automatically generate time multiplexedmulti-channel circuits from single-channel circuits are described here.

At least one embodiment of the present invention automatically andefficiently synthesize multi-channel hardware for time-multiplexedresource sharing by automatically generating a time multiplexed designof multi-channel circuits from the design of a single-channel circuit.Channel specific elements of the single-channel design (e.g., registersand memories) are replaced with corresponding elements of N-times morecapacity for pipelining the signal processing for multiple channels.

In one aspect of the invention, a method to design a digital circuitincludes: receiving a first design of a single-channel circuit; andautomatically transforming the single-channel design to generate asecond design of a time multiplexed multi-channel circuit. In oneexample, retiming is performed on the time multiplexed multi-channelcircuit after the automatic generation of the multi-channel circuit(e.g., for improving clock frequency) In one example, a pipelineregister set in the time multiplexed multi-channel circuit areidentified and removed (e.g., to adjust the latency of the multi-channelcircuit). In one example, a pipeline register set is inserted into thetime multiplexed multi-channel circuit. In one example, an multi-stateFinite-State-Machine (FSM) is generated to time multiplex access tologic elements of the first design by multiple channels; a multiplexingcircuit is generated to time multiplex multiple inputs for the multiplechannels onto an input line of the first design; and, a de-multiplexingcircuit is generated to time de-multiplex signals from an output line inthe first design into multiple outputs for the multiple channels. In oneexample, an element (e.g., a constant, a Random Access Memory (RAM)element, a Read Only Memory (ROM) element, a register, a flip-flop, or anegative latency register) in the first design is replaced with multipleor larger corresponding elements, each of which is accessed for one ofthe multiple channels according to the state of the FSM. In one example,after non-channel-specific sequential elements are identified, othersequential elements in the first design are identified aschannel-specific; and, only channel-specific elements are replaced withmultiple corresponding elements. The non-channel-specific sequentialelements include sets of pipeline register (e.g., identified fromdetermining a number of feed-forward cutsets of sequential elements asnon-channel-specific sequential elements). In one example, thechannel-specific sequential element is replaced with a cascade ofmultiple shifting sequential elements; in another example, thechannel-specific sequential element is replaced with multiple memoryelements, or a memory element with larger capacity, addressed accordingto the state of the FSM.

In one example, a sequential element (e.g., a flip-flop, a register, amemory element, a constant, and a negative latency register) in thefirst design is replaced with corresponding elements (e.g., a cascade ofregisters, a dual-port RAM or a RAM-shift register combo) to generatethe second design. The corresponding elements are sequentially accessedin the second design according to timing for processing signals frommultiple channels. In one example, the corresponding elements are acascade of shifting elements; in another example, the correspondingelements are addressed sequentially (e.g., a memory of N memory elementsis replaced with a memory with N×M memory elements for an M-channelcircuit).

In one aspect of the invention, a method to design a digital circuitincludes: receiving a first design of a single-channel circuit;generating a conglomerate of single-channel circuits of the first designand information indicating a parallelism in the conglomerate ofsingle-channel circuits; and applying a folding transformation to theconglomerate of single-channel circuits using the information togenerate a second design of time multiplexed multi-channel circuit. Forexample, the information includes information of a folding set; and, theinformation of folding set is used to guide a folding algorithm toperform the folding transformation. The first design of thesingle-channel circuit may contain negative latency registers; and, aretiming operation can be performed after the transformation.

The present invention includes methods and apparatuses which performthese methods, including data processing systems which perform thesemethods, and computer readable media which when executed on dataprocessing systems cause the systems to perform these methods.

Other features of the present invention will be apparent from theaccompanying drawings and from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings in which likereferences indicate similar elements.

FIG. 1 shows a block diagram example of a data processing system whichmay be used with the present invention.

FIG. 2 shows an example of a single-channel three-tap Finite ImpulseResponse (FIR) filter from which a multi-channel filter can beautomatically generated according to one embodiment of the presentinvention.

FIG. 3 shows signal waveforms at various locations in the example ofFIG. 2.

FIG. 4 shows an example of a two-channel filter corresponding to theconglomerate of single-channel filters of FIG. 2.

FIG. 5 shows an example of a two-channel filter automatically generatedfrom the single-channel filter of FIG. 2 according to one embodiment ofthe present invention.

FIG. 6 shows signal waveforms at various locations in the example ofFIG. 5.

FIG. 7 shows an example of a multi-channel filter automaticallygenerated from the single-channel filter of FIG. 2 according to oneembodiment of the present invention.

FIG. 8 shows an example of an output decoder and latch circuit forde-multiplexing outputs from a multi-channel filter according to oneembodiment of the present invention.

FIG. 9 shows another example of a multi-channel filter automaticallygenerated from the single-channel filter of FIG. 2 according to analternative embodiment of the present invention.

FIG. 10 shows an example of a single-channel three-tap Finite ImpulseResponse (FIR) filter with pipeline registers from which a multi-channelfilter can be automatically generated according to one embodiment of thepresent invention.

FIG. 11 shows an example of a multi-channel filter automaticallygenerated from the single-channel filter of FIG. 10 according to oneembodiment of the present invention.

FIG. 12 shows another example of a single-channel circuit with pipelineregisters from which a multi-channel filter can be automaticallygenerated according to one embodiment of the present invention.

FIG. 13 shows an example of a multi-channel filter automaticallygenerated from the single-channel filter of FIG. 12 according to oneembodiment of the present invention.

FIG. 14 shows a flow chart of a method to generate a multi-channelcircuit from a single-channel circuit according to one embodiment of thepresent invention.

FIG. 15 shows a detailed flow chart of a method to generate amulti-channel circuit from a single-channel circuit according to oneembodiment of the present invention.

FIG. 16 shows an example method to generate a multi-channel circuit froma single-channel circuit according to one embodiment of the presentinvention.

FIGS. 17-21 illustrate examples of generating a multi-channel circuitfrom a single-channel circuit with negative latency registers accordingto one embodiment of the present invention.

FIGS. 22-25 illustrate another example of generating a multi-channelcircuit from a single-channel circuit using negative latency registersaccording to one embodiment of the present invention.

DETAILED DESCRIPTION

The following description and drawings are illustrative of the inventionand are not to be construed as limiting the invention. Numerous specificdetails are described to provide a thorough understanding of the presentinvention. However, in certain instances, well known or conventionaldetails are not described in order to avoid obscuring the description ofthe present invention. References to an or one embodiment in the presentdisclosure are not necessary to the same embodiment; and, suchreferences means at least one.

At least one embodiment of the present invention seeks to automaticallyand efficiently synthesize multi-channel hardware for time-multiplexedresource sharing by automatically generating a time-multiplexed designof multi-channel circuits from the design of a single-channel circuit.

The complexity of hardware synthesis grows super-linearly with thenumber of logic units involved in the design. A multi-channel circuittypically has independent and identical single channels. An N-channelcircuit typically requires N times more logical (computational) unitsthan its single-channel counterpart in optimizing the circuit duringhardware synthesis. When a conventional folding transformation isapplied on the multi-channel circuit to generate a time multiplexedcircuit in order to reduce the function units used, the conventionalfolding algorithm spends a significant amount of time in extractingparallelism and dependencies and in optimizing computation schedules.Thus, hardware synthesis optimization for time-multiplexed resourcesharing is typically computationally intensive, particularly for largedesigns.

According to one embodiment of the present invention, the synthesisoptimization for time-multiplexed resource sharing for multiple channelsis based on the design of a single channel. The computation forextracting parallelism and dependencies is avoided; and, a design withtime-multiplexed resource sharing can be generated from the design of asingle channel without the extensive computation of the conventionalfolding transformation. In one example, a single-channel design istransformed into a time-multiplexed N-channel design by replacingchannel specific elements of the single-channel design (e.g., registersand memories) with their counterparts having N-times more capacity topipeline the signal processing for multiple channels. More examples anddetails are described below.

Many of the methods of the present invention may be performed with adigital processing system, such as a conventional, general-purposecomputer system. Special purpose computers, which are designed orprogrammed to perform only one function, may also be used.

FIG. 1 shows one example of a typical computer system which may be usedwith the present invention. Note that while FIG. 1 illustrates variouscomponents of a computer system, it is not intended to represent anyparticular architecture or manner of interconnecting the components assuch details are not germane to the present invention. It will also beappreciated that network computers and other data processing systemswhich have fewer components or perhaps more components may also be usedwith the present invention. The computer system of FIG. 1 may, forexample, be a Sun workstation, or a personal computer (PC) running aWindows operating system, or an Apple Macintosh computer.

As shown in FIG. 1, the computer system 101, which is a form of a dataprocessing system, includes a bus 102 which is coupled to amicroprocessor 103 and a ROM 107 and volatile RAM 105 and a non-volatilememory 106. The microprocessor 103, which may be a G3 or G4microprocessor from Motorola, Inc. or IBM is coupled to cache memory 104as shown in the example of FIG. 1. The bus 102 interconnects thesevarious components together and also interconnects these components 103,107, 105, and 106 to a display controller and display device 108 and toperipheral devices such as input/output (I/O) devices which may be mice,keyboards, modems, network interfaces, printers, scanners, video camerasand other devices which are well known in the art. Typically, theinput/output devices 110 are coupled to the system through input/outputcontrollers 109. The volatile RAM 105 is typically implemented asdynamic RAM (DRAM) which requires power continually in order to refreshor maintain the data in the memory. The non-volatile memory 106 istypically a magnetic hard drive or a magnetic optical drive or anoptical drive or a DVD RAM or other type of memory systems whichmaintain data even after power is removed from the system. Typically,the non-volatile memory will also be a random access memory althoughthis is not required. While FIG. 1 shows that the non-volatile memory isa local device coupled directly to the rest of the components in thedata processing system, it will be appreciated that the presentinvention may utilize a non-volatile memory which is remote from thesystem, such as a network storage device which is coupled to the dataprocessing system through a network interface such as a modem orEthernet interface. The bus 102 may include one or more buses connectedto each other through various bridges, controllers and/or adapters as iswell known in the art. In one embodiment the I/O controller 109 includesa USB (Universal Serial Bus) adapter for controlling USB peripherals,and/or an IEEE-1394 bus adapter for controlling IEEE-1394 peripherals.

It will be apparent from this description that aspects of the presentinvention may be embodied, at least in part, in software. That is, thetechniques may be carried out in a computer system or other dataprocessing system in response to its processor, such as amicroprocessor, executing sequences of instructions contained in amemory, such as ROM 107, volatile RAM 105, non-volatile memory 106,cache 104 or a remote storage device. In various embodiments, hardwiredcircuitry may be used in combination with software instructions toimplement the present invention. Thus, the techniques are not limited toany specific combination of hardware circuitry and software nor to anyparticular source for the instructions executed by the data processingsystem. In addition, throughout this description, various functions andoperations are described as being performed by or caused by softwarecode to simplify description. However, those skilled in the art willrecognize what is meant by such expressions is that the functions resultfrom execution of the code by a processor, such as the microprocessor103.

A machine readable medium can be used to store software and data whichwhen executed by a data processing system causes the system to performvarious methods of the present invention. This executable software anddata may be stored in various places including for example ROM 107,volatile RAM 105, non-volatile memory 106 and/or cache 104 as shown inFIG. 1. Portions of this software and/or data may be stored in any oneof these storage devices.

Thus, a machine readable medium includes any mechanism that provides(i.e., stores and/or transmits) information in a form accessible by amachine (e.g., a computer, network device, personal digital assistant,manufacturing tool, any device with a set of one or more processors,etc.). For example, a machine readable medium includesrecordable/non-recordable media (e.g., read only memory (ROM); randomaccess memory (RAM); magnetic disk storage media; optical storage media;flash memory devices; etc.), as well as electrical, optical, acousticalor other forms of propagated signals (e.g., carrier waves, infraredsignals, digital signals, etc.); etc.

FIG. 2 shows an example of a single-channel three-tap Finite ImpulseResponse (FIR) filter from which a multi-channel filter can beautomatically generated according to one embodiment of the presentinvention. Single-channel circuit 200 receives input on line 201 togenerate output on line 203. The single-channel design includesconstants 211, 213 and 215, multipliers 221, 223 and 225, adders 235 and237, and registers (flip-flops) 231 and 233. Input on line 201 ismultiplied by multipliers 221, 223 and 225 with constants 211, 213 and215; and, adders 235 and 237 sum the results to generate output on line203. Clock signal C_(S) on line 205 controls the pipelining and thesynchronization of the processing in the single-channel circuit.

FIG. 3 shows signal waveforms at various locations in the example ofFIG. 2. At time t₀ (301), input signal I₁ arrives on line 201. At timet₁ (303), register 231 outputs the result of multiplier 221 to generatesignal S_(A) 313 on line A 207. At time t₂ (305), register 233 outputsthe result of adder 235 to generate signal S_(B) 315 on line B 209,which is the sum of signal S_(A) 313 and the output of multiplier 223.At time t₃, adder 237 sums signal S_(B) 315 and the output of multiplier225 to generate signal O₁ 317 on output line 203.

FIG. 4 shows an example of a two-channel filter corresponding to theconglomerate of single-channel filters of FIG. 2. For example, circuits401 and 403 have the same elements and structure as circuit 200 in FIG.2. The conventional solutions for the automatic synthesis of hardwaresystems do not handle multi-channel systems specially. The conventionalmethods treat a multi-channel design as a large conglomerate ofsingle-channel systems. A conventional method typically presents thetwo-channel filter as shown in FIG. 4 without any indication of theinherent high level parallelism in the design. Thus, a hardwaresynthesis software program performs the computational intensive task ofextracting parallelism and dependencies. To generate a design withtime-multiplexed resource sharing, a folding transformation may beapplied. Thus, the conventional method is computational intensive.Further, when a multi-channel system is interpreted as a conglomerate ofsingle-channel systems, the inherent high level parallelism can bemissed, resulting in spending much more computational resources inapplying folding transformations and/or failure to sufficiently optimizethe given design.

In one embodiment of the present invention, information related to theparallelism in a conglomerate of single-channel systems, which isautomatically generated from the single channel design, is alsogenerated to guide a general folding algorithm to apply foldingtransformation in automatically transforming the a conglomerate ofsingle-channel systems into a time multiplexed circuit. For example, ina typical folding algorithm (e.g., those described in “VLSI digitalsignal processing systems: design and implementation”, by Keshab K.Parhi, Wiley-Interscience, 1999, pp. 149-187, and others), it is a timeconsuming operation to identify folding sets. A folding set is a set ofoperations that is to be executed by a same functional unit through timemultiplexing. When the conglomerate of single-channel systems isautomatically generated from the single channel design, the folding setscan be generate without extensive computation. Such identified foldingsets can be used to guide a typical folding algorithm in transformingthe conglomerate of single-channel systems (e.g., traditional foldingalgorithms can be modified to use such information for efficientoperations).

Instead of applying folding transformations to a large conglomerate ofsingle-channel systems, at least one embodiment of the present inventionexplores fully the parallelism in the multi-channel circuits by applyingautomated transformations on the single-channel design to generate adesign that enables time multiplexed resource sharing.

One embodiment of the present invention presumes multi-channel behaviorfrom the beginning to avoid spending time in extracting parallelism anddependencies and in optimizing computation schedules, etc. Taking thesingle-channel version of the system as the input, it applies a simplemapping to make very effective use of the high level parallelisminherent in the multi-channel system. Since the data flows within theseparate threads of the resulting multi-channel design are identical,the resulting control circuitry is minimal.

FIG. 5 shows an example of a two-channel filter automatically generatedfrom the single-channel filter of FIG. 2 according to one embodiment ofthe present invention. Functional units (e.g., multipliers and adders)are not channel specific. Since constants C1, C2, and C3 (211, 213 and215) are not channel specific, they can also be shared withoutmodification. Registers are in this case channel specific. Thus,registers 231 and 233 of single-channel design 200 are replaced withcascades of 2-shift registers 531, 533 and 535, 537. Inputs 501 and 503(e.g., corresponding to inputs 411 and 413 of channel 401 and 403 inFIG. 4) are time multiplexed by multiplexer 541 onto input line 505according to signal S_(M) (507); and, output 509 is de-multiplexed byde-multiplexer 543 onto lines 513 and 515 (e.g., corresponding tooutputs 421 and 423 of channel 401 and 403 in FIG. 4). It is understoodthat the generation of multiplexer 541 (or de-multiplexer 543) isoptional, depending whether or not the multiple-channel receives (orgenerates) signals on multiple ports.

FIG. 6 shows signal waveforms at various locations in the example ofFIG. 5. Input signals I₁ (615) and I₂ (617) are time multiplexed assignal S_(I) according to the state of control signal S_(M) (613). In atypical clock cycle of the single-channel circuit (e.g., from time t₀301 to t₁ 303 in FIG. 3, which correspond to time t₀ 601 to t₂ 603 inFIG. 6), each input signal is assigned to one time slot (e.g., slot 621for signal I₁ 615 and slot 622 for signal I₂ 617). The input signalassigned for a given slot is processed by the logic units and pipelinedby the cascades of registers for further processing. For example, signalI₁ 615 assigned to slot 621 in S_(I) is multiplied by constant 211 togenerate intermediate result 631 in S_(A1) at time t₁ on line A1 (521)from register 531. Intermediate result 631 is delayed by register 533 tooutput signal 641 in S_(A2) on line A2 (523) at time t₂ 603, after whichsignal I₁ 615 is again assigned slot 623 in S₁ as input for multiplier223. At time t₃ 604, the result of adder 235 is output from registers535 to generate on line B1 (525) signal 651 in S_(B1), which issimilarly delayed by register 537 to output on line B2 (527) signal 661in SB2 at time t₄ 605, after which signal I₁ 615 is again assigned slot625 in S₁ as input for multiplier 225. At time t₅ 606, signal 671 ofS_(O) on line O (509 in FIG. 5), the result from adder 237 for inputsignal I₁ 615, is ready for output by de-multiplexer 513. Similarly,signal 672 is the result of input signal I₂ 617, computed from the inputassigned to slots 622, 624 and 626. Further, the intermediate resultsfrom previous inputs are pipelined in the system so that results basedon the previous inputs are available in the intermediate next clockcycles (e.g., results based on samples 623, 625 and 627 of input I₁ isavailable at time slot 673).

Thus, FIGS. 5 and 6 illustrate that, when a register in thesingle-channel design is replaced by a cascade of registers, theintermediate result stored in the register of the single-channel designis pipelined in the cascade of registers in the multi-channel design sothat the output the cascade of registers is synchronized with the timeslot assignment for the signal processing in the multi-channel circuit.In one embodiment of the present invention, each of the channel-specificsequential elements (e.g., registers, flip-flops, memory elements) inthe single-channel design is replaced with corresponding elements ofN-times more capacity (e.g., a cascade of registers or flip-flops,dual-port RAM addressed according to the time slot assignment, RAM-shiftregister combo, and others).

FIG. 7 shows an example of a multi-channel filter automaticallygenerated from the single-channel filter of FIG. 2 according to oneembodiment of the present invention. To automatically convertsingle-channel design 200 of FIG. 2 into time multiplexed N-channeldesign 700 of FIG. 7, register 231 of FIG. 2 is replaced with a cascadeof N-shift registers 711-719; and, register 233 of FIG. 2 is replacedwith a cascade of N-shift registers 721-729. Modulo-N counter 705 isused to generate a signal for controlling the time slot assignment forinput signals. When the output of modulo-N counter 705 on line 707 is i(i=0, 1, . . . , N−1), multiplexer 701 selects signal I_(i+1) as theinput signal to line 709. Similarly, the output signal from adder 237 inFIG. 7 is decoded by de-multiplexer 703 to generate output signals forcorresponding channels according to the output of modulo-N counter 705.

FIG. 8 shows an example of an output decoder and latch circuit forde-multiplexing outputs from a multi-channel filter according to oneembodiment of the present invention. Testers 811, 813, . . . , 819control latches 801, 803, . . . , 809 according to the state ofselection signal 841 (e.g., from modulo-N counter 705 of FIG. 7). Thesignal on line 843 (e.g., the output of adder 237 of FIG. 7) is latchedon one of output lines 831, 833, . . . , 839, when the state of theselection signal matches the corresponding one of the constants(821-829) for the testers (811-819).

FIG. 9 shows another example of a multi-channel filter automaticallygenerated from the single-channel filter of FIG. 2 according to analternative embodiment of the present invention. In FIG. 9, circuit 200is accessed in a round-robin fashion to process each of the inputsignals. Modulo-3 counter 907 allows input signals for each of thechannels to be completely processed to generate an output signal beforethe channel is used for the processing of the signals of the nextchannel. Modulo-N counter 905 selects the signals of the channel to beprocessed by circuit 200. Although the method of FIG. 9 makes fewermodifications to the single-channel circuit in generating themulti-channel design, the circuit of FIG. 9 has a smaller throughputthan the circuit of FIG. 7. The signal pipelining in the single-channeldesign is not fully utilized in FIG. 9 because of the round-robinscheme. Depending on the structure of the input and output signals, thelatency for the processing of signals for each channel may be minimizedwhen a multi-channel design of FIG. 9 is used. However, it is understoodthat, in general, the input signals for different channels do not arrivein a round-robin fashion; instead, the input signals for differentchannels arrive at the same time. To retiming the input signals so thatthe input signals arrive in a round-robin fashion, a buffer can be usedbetween the input signal and multiplexer 901. Such a buffer samplesinput signals at the same time, but delays the input signals fromdifferent channels for different amount of time so that the sampledsignals arrived at multiplexer 901 in a round-robin fashion.

It is noticed that the time-multiplexed multi-channel of FIG. 7 can beused directly to replace the conglomerate of single-channel systems(e.g., in FIG. 4) when the frequency of the clock signal C_(N) (741) isN times the frequency of the clock signal of the single-channel systems(e.g., clock signal C_(S) 431 of FIG. 4). When a design of FIG. 9 isused, an additional circuitry (e.g., a block of RAM with addressedaccording to the timing of the input signals and the time slotassignment for processing) can be used to retime the inputs.

In one embodiment of the present invention, each of the channel-specificelements (e.g., registers, constants, ROM or RAM) of the single-channeldesign is replaced with corresponding elements to pipeline theprocessing for multi-channel inputs. Although each of the registers (orflip-flops) can be considered a channel-specific register, which isreplaced with a cascade of shifting registers, pipeline registers can beidentified as non-channel-specific registers. When the pipelineregisters are not replaced with cascade of shifting registers, thetiming within the time-multiplexed shared channel can still besynchronized with respect to the input of the channels.

A set of pipeline registers is a feed-forward cutset of the systemgraph. As a feed-forward cutset of the system, the removal of the set ofpipeline registers partitions the system into two disconnectedsubsystems, with a unidirectional flow of data between the twosubsystems. However, when there are multiple inputs and/or multipleoutputs in the system, the cutset that partitions the inputs intodifferent subsystems or the outputs into different subsystems does notqualify as a set of pipeline registers, since synchronization can bedistorted if such a cutset is not pipelined in generating themulti-channel design.

Feed-forward cutsets can be automatically identified using variousalgorithms known in the art. For example, Eran Halperin and Uri Zwickdescribed methods in “Combinatorial approximation algorithms for themaximum directed cut problem”, Proceedings of 12th Symposium on DiscreteAlgorithms, pp. 1-7, 2001, which can be used to determine thefeed-forward cutsets. It is noticed that feed-forward cutsets are oftenreferred to as “directed cuts” (or “dicuts”) in graph theory literature.The methods of Eran Halperin and Uri Zwick for finding “maximum directedcuts” can be used to find the feed-forward cutsets containing maximumnumbers of registers.

FIG. 10 shows an example of a single-channel three-tap Finite ImpulseResponse (FIR) filter with pipeline registers from which a multi-channelfilter can be automatically generated according to one embodiment of thepresent invention. The design of FIG. 10 includes pipeline registers1001-1005. Feed-forward cutset 1011 partitions the system of FIG. 10into two subsystems with a unidirectional flow of data between the twosubsystems. Thus, registers 1001-1005 are identified asnon-channel-specific; and thus, the channel-specific elements in thedesign of FIG. 10 are registers 231 and 233. Channel specific registers231 and 233 in FIG. 10 are replaced with cascades of registers togenerate time-multiplexed resource shared design of FIG. 11.

FIG. 11 shows an example of a multi-channel filter automaticallygenerated from the single-channel filter of FIG. 10 according to oneembodiment of the present invention. In FIG. 11, pipeline registers 1011remain unchanged. To synchronize the operation of the de-multiplexer 703with the state of Modulo-N counter 705, register 1201 is inserted todelay the output of counter 705 for one cycle to offset the effect ofthe delay caused by cutset 1011. In general, when M sets of pipelineregisters are identified as non-channel specific elements, the output ofthe Modulo-N counter is delayed mod(M, N) cycles to synchronized theoperations of multiplexer and de-multiplexer (e.g., 701 and 703 in FIG.11). It is also notice that registers 231, 1003 and 1005 in FIG. 10 canbe identified as a set of pipeline registers, in which case registers1001 and 233 will be replaced with cascades of shifting registers.Alternatively, if none of the registers in FIG. 10 is identified aspipeline registers, all registers in FIG. 10 are replaced with cascadesof registers, in which case the resulting design will have N sets ofpipeline registers and no register is necessary to delay the output ofmodulo-N counter 705, since mod(N,N)=0.

A channel-specific register of the single-channel system can be replacedwith a cascade of N-shift registers in generating the multi-channelsystem. In some FPGA architectures (such as Xilinx Virtex), shiftregisters are natural primitives. This enables very efficient memoryusage when the target architecture is one of these FPGA architectures.It is understand that each of the channel-specific registers can be alsobe replaced by other memory structures (e.g., an N-item dual-port RAM,or a RAM-shift register combo, or others) that can pipeline theintermediate results according to the state of the module-N counter.

FIG. 12 shows another example of a single-channel circuit with pipelineregisters from which a multi-channel filter can be automaticallygenerated according to one embodiment of the present invention. Thedesign of FIG. 12 contains feed-forward cutsets 1211 and 1213, includingregisters 1201, 1203, 231 and 1205, 233. Thus, all registers in FIG. 12can be identified as non-channel specific; and, no register is replacedwith a cascade of registers in generating the design of FIG. 13.

FIG. 13 shows an example of a multi-channel filter automaticallygenerated from the single-channel design of FIG. 12 according to oneembodiment of the present invention. Since there are two sets ofpipeline registers between multiplexer 1301 and de-multiplexer 1303, twocycles of delay can be used to synchronize the operations of themulti-channel filter. The design of FIG. 13 rotates the constants ofde-multiplexer 1303 for two shifts to compensate the delay caused by thetwo sets of pipeline registers. Thus, when modulo-N counter outputs i(i=0, 1, . . . , N−1), multiplexer 1301 selects signal I_(i+1) as theinput while de-multiplexer 1303 outputs for O_(mod(i−1,N)).

From the above examples, it will be apparent to one skilled in the artthat different methods (e.g., inserting delay elements, shiftingconstants for the de-multiplexer, generating different selectionsignals, or combination of these) can be used to compensate the delayscaused by the sets of pipeline registers that remain unchanged in thetime-shared design. Further, in general, a Finite State Machine (FSM)(e.g., a modulo-N counter) can be used to control the time multiplexingof the input signals, as well as the resource sharing in the design.

Although the above examples are illustrated using a single-channeldesign with a single input and a single output, from this description,it will be apparent to one skilled in the art that methods of variousembodiments of the present invention can also be applied to asingle-channel design with multiple inputs and multiple outputs.Further, an M-channel design (M>1) can be treated as a single-channeldesign to automatically generate an N×M-channel design with resourcesharing.

In one embodiment of the present invention, the single-channel design isoptimized before and/or after the automatic transformation in generatingthe resource shared design for multiple channels using conventionalmethods (e.g., folding transformation, and others).

FIG. 14 shows a flow chart of a method to generate a multi-channelcircuit from a single-channel circuit according to one embodiment of thepresent invention. After a single-channel design is received inoperation 1401, operation 1403 automatically transforms thesingle-channel design to generate a time multiplexed multi-channeldesign. Since the transformation is based on a single-channel design,which has fewer logical elements than a conglomerate of single-channelsystems, computational intensive operations of extracting high levelparallelism are avoided.

FIG. 15 shows a detailed flow chart of a method to generate amulti-channel circuit from a single-channel circuit according to oneembodiment of the present invention. Operation 1501 receives a design ofa single-channel circuit. Operation 1503 generates an N-statefinite-state-machine (FSM) (e.g., a Modulo-N counter) to time multiplexaccess to the logic elements of the single-channel circuit. Operation1505 generates a multiplexing circuit to multiplex, according to thestate of the FSM, N-channel inputs as the input to the single-channelcircuit. Operation 1507 replaces each channel-specific element (e.g.,RAM, ROM, constants, registers, flip-flops) of the single-channelcircuit with corresponding elements that are accessed for multiplechannels according to the state of the FSM. Operation 1509 generates ade-multiplexing circuit to de-multiplex, according to the state of theFSM, from the corresponding output of the single-channel circuit intoN-channel outputs. After the above transformation, a multi-channeldesign is generated from the single-channel design.

FIG. 16 shows an example method to generate a multi-channel circuit froma single-channel circuit according to one embodiment of the presentinvention. Operation 1601 receives a design of a single-channel circuit.Operation 1603 generates a modulo-N counter to control the logicelements of the single-channel to perform operations for the signal ofchannel i (i=0, 1, . . . , N−1) when the value in the counter is i.Operation 1605 generates an N-item multiplexer to receive the input forchannel i as the input for the single-channel circuit when the value inthe counter is i. Operation 1607 optionally identifiesnon-channel-specific sequential elements (e.g., flip-flops, registers,ROM, constant, RAM) in the single-channel circuit. Operation 1609replaces each of the channel-specific registers (e.g., flip-flop) of thesingle-channel design with N sequential elements (e.g., a cascade ofN-shift registers, an N-item dual-port RAM, or RAM-shift registercombo). Operation 1611 replaces each channel-specific memory (e.g., aRAM or ROM) of size M by a new memory of size N×M where memory itemN×j+i of the new memory is addressed for channel i when item j of thememory is addressed in the single-channel circuit. Operation 1613replaces each channel-specific constant with an N-item ROM memory wherememory item i is addressed for the constant of channel i. Operation 1615generates an N-item de-multiplexer to generate output for each channelfrom the corresponding output of the single-channel circuit.

In one embodiment of the present invention, a retiming algorithm (e.g.,cutset retiming and pipelining, retiming for clock period minimization,such as those described in “VLSI digital signal processing systems:design and implementation”, by Keshab K. Parhi, Wiley-Interscience,1999, pp. 91-118, or others known in the art) is further used to improvethe clock rate of the circuit, using the registers introduced during theautomatic generation of the multi-channel circuit.

During the process of a circuit design, a negative latency register,which has a negative delay, can be used in an intermediate stage (e.g.,in peripheral retiming, or in architectural retiming). While no physicalnegative latency register exists, it is understood that a negativelatency register indicates a timing constraint at an intermediate stateof design. Negative latency registers can be used in the early stage ofthe design process; and the negative latency registers are typicallyeliminated during the process of circuit design to achieve a finalsolution.

In one embodiment of the present invention, a single-channel system isspecified with one or more negative latency registers; and, the negativelatency registers can be transformed in a similar fashion as the regularregisters.

FIG. 17 shows an example of a single-channel system. For the purpose ofillustration, the latency of elements other than registers is ignored.Each register (e.g., 1731, 1733 and 1741) has a one-unit latency.Elements 1711, 1713 and 1715 are constants, which do not change in time.Thus, assuming the input on line 1701 is I₁(t), the signal on line 1703is I₁(t)×C₃+I₁(t−2)×C₂+I₁(t−2)×C₁. In FIG. 17, register 1731 stores theintermediate result from multiplier 1721 to generate I₁(t−1)×C₁; and,register 1733 stores the intermediate result from multiplier 1723 togenerate I₁(t−1)×C₁. Register 1741 stores the intermediate result fromadder 1751 to generate I₁(t×2)×C₂+I₁(t−2)×C₁.

A pair of positive and negative latency registers can be inserted intopath between multiplier 1725 and adder 1753. After the insertion, thecircuit in FIG. 17 is transformed to that in FIG. 18. In FIG. 18,register 1743 is a negative latency register; and, register 1735 is aregular register (positive latency register). It is seen that in FIG. 18registers 1731, 1733 and 1735 is a set of pipeline register. Note thatthe removal of the set of pipeline register (1731, 1733 and 1735)changes the latency of the signal-channel circuit (which may beacceptable or desirable in some instances); alternatively, a register(not shown in FIG. 19) can be inserted before point 1701 in FIG. 19 tohave a single-channel circuit that has the same latency as that of thecircuit in FIG. 18. Thus, the single-channel circuit in FIG. 18 can bespecified as that in FIG. 19. In FIG. 19, assuming the input on line1701 is I₁(t), the output on line 1703 isI₁(t+1)×C₃+I₁(t−1)×C₂+I₁(t−1)×C₁. Thus, apart from a one-unit timingshift, the circuit in FIG. 19 performs essentially the function as thecircuit in FIG. 17 (or FIG. 18). When the circuit in FIG. 19 isspecified as an input, a multi-channel circuit can be automaticallygenerated. Registers 1741 and 1743 are not pipeline registers; and, theycan be replace with multiple cascaded registers. FIG. 20 shows anexample of a two-channel circuit automatically generated from the inputof FIG. 19. Negative latency register 1743 in FIG. 19 is replaced withcascaded negative latency registers 1771 and 1773; and, register 1741 inFIG. 19 is replaced with cascaded registers 1761 and 1763. Multiplexer1705 is added to feed the input signals into the shared channel one at atime; and, demultiplexer 1707 is added to restore the output from theshared channel one at a time. After the generation of the multi-channelcircuit, a retiming algorithm (e.g., those described in “VLSI digitalsignal processing systems: design and implementation”, by Keshab K.Parhi, Wiley-Interscience, 1999, pp. 91-118, or others known in the art)can be used to optimize the system. For example, pipeline register setscan be inserted into eliminate the negative latency registers. Forexample, two pipeline register sets can be inserted after multipliers1721, 1723 and 1725 to generate the circuit in FIG. 21. Note that, asdescribed previously, the insertion or deletion of pipeline registersets can change the timing for the generation of output on line 1703 ingeneral; and thus, a proper number of registers (or delay elements) canbe used on line 1709 to adjust the timing of the control signal for thedemultiplexer 1707 (as illustrated in FIG. 11), the correspondencebetween the control signal and the output line can be adjusted (asillustrated in FIG. 13). It is seen that the circuit in FIG. 21 can begenerated directly from the circuit of FIG. 17, according to embodimentsof the present invention. Note that the two pipeline register sets canalso be inserted after multipliers 1725 and adder 1751 in FIG. 20 toeliminate negative latency registers.

Further, in one embodiment of the present invention, one or more pairsof positive and negative latency registers are introduced into thesingle-channel system in the process of identifying pipeline registers.For example, after the single-channel circuit of FIG. 17 is received forthe generation of multi-channel circuit, a positive and negative latencyregister pair (e.g., 1735 and 1743 in FIG. 18) is inserted foridentifying pipeline registers. As illustrated in FIG. 18, once regularregister 1735 and negative latency register 1743 are inserted, pipelineregister sets (1731, 1733 and 1735) can be identified. Thus, onlyregisters 1741 and 1743 of FIG. 18 are replaced with correspondingcascaded registers. Similarly, retiming algorithms can be used tofurther optimize the circuit of the automatic generation of themulti-channel circuit.

FIGS. 22-25 illustrate another example of generating a multi-channelcircuit from a single-channel circuit using negative latency registersaccording to one embodiment of the present invention. The single-channelfilter of FIG. 22 has pipelined adder 1847 (A₂) and pipelinedmultipliers 1841-1843 (M₁-M₃). A pipelined adder has an embeddedregister. For example, pipelined adder 1847 has register 1865, which isa physical part of the pipelined adder and cannot be moved out.Similarly, a pipelined multiplier also has an embedded register (e.g.,pipelined multipliers 1841, 1842 and 1843 has registers 1831, 1833 and1835 respectively).

Consider that a pipelined adder is to be used to implement adder 1851.Without using a negative latency register, a set of regular registersmay be added (e.g., on both the input lines for adder 1853) to provideadder 1851 a register. Such an approach can lead to the increase of thelatency of the single channel system. Alternatively, FIG. 23 shows anexample in which a pair of positive and negative latency registers (1861and 1863) are added between adders 1851 and 1853. Thus, adder 1851 andregister 1861 can be implemented as a pipelined adder 1845 (A₁). Notethat negative latency register cannot be eliminated in thesingle-channel system even with retiming.

A multi-channel circuit can be automatically generated according toembodiments of the present invention. For example, FIG. 23 shows thetime-shared portion of a multi-channel circuit, generated according toone embodiment of the present invention for a two-channel circuit. Notethat the input multiplexing portion and the output de-multiplexingportion of the two-channel circuit are not shown in FIG. 24. Registers1831, 1833 and 1835 are channel specific in FIG. 23; and, registers1832, 1834 and 1836 are inserted in FIG. 24 for the multi-channelcircuit. Similarly, registers 1861 and 1863 in FIG. 23 are replaced withcascaded register sets (1861,1862 and 1863 and 1864) in FIG. 24.

In the two-channel circuit generated according to one embodiment of thepresent invention, extra registers are generated for each of thepipelined operators. And, a retiming operation can be used to remove thenegative registers. For example, registers 1832 and 1834 in FIG. 24 canbe moved to the path between adders 1851 and 1853 in a retimingoperation so that there are sufficient regular registers on the pathbetween adders 1851 and 1853 to cancel out the negative registers (1863and 1864). Thus, an example resulting two-channel circuit is shown inFIG. 25. In FIG. 25, multipliers 2821, 1823 and 1825 and adders 1851 and1853 can be implemented as corresponding pipelined operators (pipelinedmultipliers 1841, 1842 and 1843 and pipelined adders 1845 and 1847).However, all negative latency registers are eliminated after retiming.

Pipelined adders and pipelined multipliers are illustrated in the aboveexample. However, from this description, it will be appreciated thatother pipelined logic elements or pipelined IP blocks can also betreated in a similar fashion.

In one embodiment of the present invention, no pipeline register setsare identified; and, all registers are considered as channel-specific.For example, an automatic method to transform a single-channel systeminto an N-channel system includes the following operations.

1. Generate a modulo-N counter as an N-state finite-state-machine (FSM).The state variable of the FSM is denoted as cnt. The m′th channel(0≦m≦N−1) of the system is effectively activated when the FSM is in them′th state (e.g., when cnt=m).

2. Replace each register by a cascade of N-shift registers (oralternatively, if N is large, each register can be replaced with anN-item dual-port RAM or a RAM-shift register combo).

3. Replace each RAM memory of size M by a RAM memory of size N×M. Theaddress generation circuitry is modified or added to address the memoryitems such that memory item A of the single-channel design is replacedby an item at address N×A+cnt. It is understood that other addresstransformation scheme can also be used to logically pipeline memoryitems so that the output from the new memory is synchronized with thestate of the FSM. The transformed address is typically a function of theoriginal address, the state of the FSM, and the active channel number.

4. When there is a channel-specific ROM (e.g., ROM contents vary fromchannel to channel), apply a transform similar to that for the RAM sothat ROM item N×A+m holds the contents of the ROM item A for m'thchannel. If the ROM is not channel specific, no transformation isnecessary.

5. If there is a channel-specific constant (e.g., constant value variesfrom channel to channel), replace it with an N-item ROM. The addressline of the ROM is driven by cnt (or cnt−1 if there is one clock latencyin ROM access). If the constant is not channel specific, notransformation is necessary.

The inputs of the different channels may be multiplexed over a commonport. If multiple channels have their distinct input ports, multiplexthese inputs by an N-item multiplexer with a selection line driven bycnt, which is N-times faster than the clock driving the inputs.Similarly, the outputs of the different channels may be multiplexed overa common port. If multiple channels have their distinct output ports,de-multiplex the outputs by an N-item decoder with a selection linedriven by cnt. The outputs can be latched with an N-times slower clock.The other components of the single-channel design are kept as is as theshared resources through time multiplexing.

In another embodiment of the present invention, pipeline register setsare identified to avoid the generation of registers. For example, anautomatic method to transform a single-channel system into an N-channelsystem includes the following operations.

1. Identify the pipeline registers in the system to cover as many and aswide registers as possible. There can be more than one set of pipelineregisters, but the sets must be mutually exclusive. Any register notclassified into any of the pipeline register sets is a state register.Pipeline registers are non-channel-specific; and, state registers arechannel-specific. If there are P distinct pipeline register sets, thesystem is partitioned into P+1 disjoint subsystems, forming a singlylinked list of subsystems. In this list, each feed-forward cutsetdefines a link, with the direction of the link indicating the directionof data flow. Denote S_(i) the subsystem whose order in the linked listis i, where 0≦i≦P.

2. Generate P+1 N-state finite-state-machines (FSMs) from at least onemodulo-N counter. Denote the state variable of i'th FSM (0≦i≦P) ascnt_(i). The hardware in subsystem S_(i) processes the data of the m'thchannel (0≦m≦N−1) when the i'th FSM is in the m'th state (e.g., whencnt_(i)=m). When mod((cnt_(i)−cnt_(j)),N)=mod ((j−i), N) for ∀i, j in[0,P], correct synchronization is maintained among the subsystems. Thisrelation is satisfied if cnt_(i) is a one-clock delayed version ofcnt_(i−1). (i=1, 2, . . . , N−1). Thus, cnt_(i) can be derived fromcnt_(i−1) using a register; and, the FSMs can be implemented using onemodulo-N counter and a cascade of registers.

3. Replace each state register with a cascade of N-shift registers (oralternatively, if N is large, each state register can be replaced withan N-item dual-port RAM or a RAM-shift register combo).

4. Replace each RAM memory of size M by a RAM memory of size N×M. For aRAM within the subsystem S_(i), the address generation circuitry ismodified or added to address the memory items such that memory item A ofthe single-channel design is replaced by an item at address N×A+cnt_(i).It is understood that other address transformation scheme can also beused to logically pipeline memory items so that the output from the newmemory is synchronized with the state of the i'th FSM. The transformedaddress is typically a function of the original address, the state ofthe i'th FSM, and the active channel number.

5. When there is a channel-specific ROM (e.g., ROM contents vary fromchannel to channel), apply a transform similar to that for the RAM sothat ROM item N×A+m holds the contents of the ROM item A for m'thchannel. If the ROM is not channel specific, no transformation isnecessary.

6. If there is a channel-specific constant (e.g., constant value variesfrom channel to channel) within the subsystem S_(i), replace it with anN-item ROM. The address line of the ROM is driven by cnt_(i) (orcnt_(i)−1 if there is one clock latency in ROM access). If the constantis not channel specific, no transformation is necessary.

The inputs of the different channels may be multiplexed over a commonport. If multiple channels have their distinct input ports, multiplexthese inputs by an N-item multiplexer with a selection line driven bycnt₀, which is N-times faster than the clock driving the inputs.Similarly, the outputs of the different channels may be multiplexed overa common port. If multiple channels have their distinct output ports,de-multiplex the outputs by an N-item decoder with a selection linedriven by cnt_(P). The outputs can be latched with an N-times slowerclock. The other components of the single-channel design are kept as isas the shared resources through time multiplexing.

Although P+1 N-state finite-state-machines can be used to control thetiming of the P+1 subsystems individually, alternatively, one singleN-state FSM can be used to control the operation of all subsystems,where different subsystems process for a given channel when the state ofthe FSM reaches different values. For example, the hardware in subsystemS_(i) processes the data of the m'th channel (0≦m≦N−1) when the FSM isin the state cnt=mod (m−i, N).

Pipeline register sets can be identified and removed, when timingconstraints permit. For example, the set of pipeline registers 1011 inFIG. 10 can be removed to generate the design of FIG. 2; or, thepipeline register set 1011 of FIG. 11 can be removed automatically togenerate the design of FIG. 7. Similarly, pipeline registers can also beadded to a design automatically. Note that the addition or deletion ofpipeline registers in general changes input to output latency of thecircuit; however, such changes are acceptable for most cases.

In one embodiment of the present invention, employing shift registerswith run-time-configurable depth and using modulo-N counters withrun-time-configurable modulus, the folding rate N can be changed inrun-time, without interrupting the operation. For the applications inwhich the number of active channels is a dynamic parameter, the foldingrate can be adapted to the number of active channels, allowing the clockrate to be reduced, when possible, to reduce the power consumption.

Thus, at least one embodiment of the present invention automaticallygenerates a design for a multi-channel system from the input of thedesign of single-channel system. The single-channel system design isautomatically transformed into an N-channel system with time-multiplexedresource sharing of logical (computational) units. The transform issimple and very fast; and, the resulting design of the hardware is veryefficient.

Since methods of various embodiment of the present invention generate atime-multiplexed multi-channel design from a single-channel design, fastoptimization and synthesis operations can be performed on the reducednumber of logic elements. The usage of control logic can be minimized.For some FPGA architectures, the memory usage of the synthesized systemcan be made very efficient. Further, various methods of the presentinvention allow for high pipeline orders and significant speed-ups.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will be evidentthat various modifications may be made thereto without departing fromthe broader spirit and scope of the invention as set forth in thefollowing claims. The specification and drawings are, accordingly, to beregarded in an illustrative sense rather than a restrictive sense.

1. A method to design a digital circuit, the method comprising:receiving a first design of a single-channel circuit; and automaticallytransforming the single-channel circuit to generate a second design of atime multiplexed multi-channel circuit.
 2. A machine readable mediumcontaining executable computer program instructions which when executedby a digital processing system cause said system to perform a method todesign a digital circuit, the method comprising: receiving a firstdesign of a single-channel circuit; and automatically transforming thesingle-channel circuit to generate a second design of a time multiplexedmulti-channel circuit.
 3. A digital processing system to design adigital circuit, the digital processing system comprising: means forreceiving a first design of a single-channel circuit; and means forautomatically transforming the single-channel circuit to generate asecond design of a time multiplexed multi-channel circuit.
 4. A methodto design a digital circuit, the method comprising: receiving a firstdesign of a single-channel circuit; generating a conglomerate ofsingle-channel circuits of the first design and information indicating aparallelism in the conglomerate of single-channel circuits; and applyinga folding transformation to the conglomerate of single-channel circuitsusing the information to generate a second design of time multiplexedmulti-channel circuit.
 5. A machine readable medium containingexecutable computer program instructions which when executed by adigital processing system cause said system to perform a method todesign a digital circuit, the method comprising: receiving a firstdesign of a single-channel circuit; generating a conglomerate ofsingle-channel circuits of the first design and information indicating aparallelism in the conglomerate of single-channel circuits; and applyinga folding transformation to the conglomerate of single-channel circuitsusing the information to generate a second design of time multiplexedmulti-channel circuit.
 6. A digital processing system to design adigital circuit, the digital processing system comprising: means forreceiving a first design of a single-channel circuit; means forgenerating a conglomerate of single-channel circuits of the first designand information indicating a parallelism in the conglomerate ofsingle-channel circuits; and means for applying a folding transformationto the conglomerate of single-channel circuits using the information togenerate a second design of time multiplexed multi-channel circuit.